Complementary metal oxide semiconductor (CMOS) technology is a building block for integrated circuits, and CMOS devices are scaled to smaller sizes for advanced performance targets. CMOS technology includes N-type metal oxide semiconductors (NMOS) and P-type metal oxide semiconductors (PMOS). For example, a metal-oxide-semiconductor field-effect transistor (MOSFET) is a transistor used for amplifying or switching electronic signals.
A CMOS transistor generally comprises a semiconductor substrate, a channel layer above the semiconductor substrate, a gate oxide layer and a gate electrode above the channel layer, and a source region and a drain region above semiconductor substrate. Contacts, such as metal plugs, are made to the gate electrode and to both the source and drain regions of the transistor.